1. Field of the Present Invention
The present disclosure relates to plasma etching methods.
2. Description of the Related Art
In producing three dimensional laminated semiconductor memories such as 3D-NAND flash memories, a method is known, in which a laminated film of a silicon oxide film and a silicon nitride film is etched through a plasma etching, thereby forming a hole or trench with high aspect ratio.
According to the method, a gap or unevenness (scallop shape) may be created at an interface between the silicon oxide film and the silicon nitride film in a case where the etching speeds for the silicon oxide film and for the silicon nitride film are different. When such a gap is created, for example, reliability of a product may decrease because the film formed on the hole or trench may be easily peeled in a later stage of the production.
Therefore, conventionally, for example, the laminated film is etched by plasma etching process using a mixture of NF3 gas and CH3F gas to suppress generation of the scalloping (e.g., Patent Document 1).
However, although the scalloping generated in the etching process of the laminated film can be suppressed according to the method of Patent Document 1, the Patent Document 1 does not disclose a method for removing the scalloping that has been already formed. Therefore, according to the conventional technology, etching shape may be degraded in a case where the scalloping is created at the interface between the silicon oxide film and the silicon nitride film during the etching process performed on the laminated film of the silicon oxide film and the silicon nitride film.
[Patent Document 1]: Japanese Laid-open Patent Publication No. 2015-144158